Nitrated organic liquid propellant composition having improved spark ignition



United States Patent Oh 3,377,219 NITRATEI) ORGANIC LIQUID PROPELLANTCOh ZPOSITIUN HAVING IMPROVED SPARK IGNITKON Ludwig Stiefel,Philadelphia,

Levittown, Pa, assignors to the United States of America as representedby the Secretary of the Army No Drawing. Filed Sept. 28, 1964, Ser. No.399,943 4 Claims. (Cl. 149*88) ABSTRACT OF THE DISCLOSURE Liquidpropellants capable of ready ignition by a submerged spark therewithin,the spark requiring but little energy to cause its formation due to thecomposition of said propellant which includes either a quaternaryammonium salt or colloidal graphite.

and Howard A. Kirshuer,

The invention described herein may be manufactured and used by or forthe Government poses without the payment to us of any royalty thereon.

This invention relates to spark ignition of liquid propellants andparticularly, to submerged spark ignition of non-conductive organicliquids used as propellants.

Many organic liquids propane, alkyl nitrates, and nitrate estercompounds are commonly employed as liquid propellants. Certainapplications of these propellants require that they be ignited byelectrical spark discharge generated across electrodes submerged in thepropellants. However, efforts to conveniently ignite the propellants bythis electrical spark discharge method have resulted in virtual failure.At the root of the problem is the very high order of electrical energyrequired for generating the ignition spark. The size and extent of theequipment necessary to provide this energy has been such as to renderthe method impractical. A principal reason advanced for the highelectrical energy required for spark ignition is the poor electricalconduction properties of the propellants.

It is, therefore, an object of this invention to provide organic liquidpropellants characterized by improved electrical conduction properties.

A further object is to provide a method for enhancing the electricalproperties of organic liquid propellants to permit practical submergedspark ignition thereof.

The above and other objects are attained by adding into organic liquidpropellants or blends thereof small amounts of either low molecularweight quaternary ammonium salts or colloidal graphite. For example,igniting 2. for governmental purincluding nitromethane, nitro- 3,377,219Patented Apr. 9, 1968 ice trate propellant having increased electricalconductivity characteristics is obtained. Accordingly, the electricalenergy required to generate the ignition spark is considerablydiminished.

The improved propellants of this invention comprise any non-conductive,organic liquid propellants to which have been added between 0.5% and3.0% by weight of an additive selected from the group consisting of aquaternary ammonium salt and colloidal graphite. In the case of theformer, dissolution occurs in the propellant while in the case of thelatter the graphite remains in suspension. However, the results in anyof the'above mixtures are the same, that is, in comparison withnon-conductive, organic liquid propellants not having the additivesmentioned, substantially lower electrical energies are necessary forgenerating ignition spark-s across electrodes submerged in thepropellants.

The following examples further illustrate the invention, which is not tobe construed as limited thereby. Various quaternary ammonium salts aswell as colloidal graphite were mixed under ambient conditions with basepropellants. The examples are shown in. thefollowing table.

TABLE I Ex. No. Base Propellant Additive and Quantity Thereof 1 EthylNitrate, 40% 1.5% b weight colloidal Propyl N itrate. graphite. 2 60%Ethyl Nitrate, 40% 1.5% by weight tetra ethyl Propyl Nitrate. ammoniumchloride. 3 60% Ethyl Nitrate, 40% 0.5% by weight tetra n- PropylNitrare. propyl ammonium nitrate. 4 100% Propyl Nitrate 3.0% by weighttetra npropyl ammonium nitrate.

To illustrate the improved spark ignition characteristics of thepropellants of this invention, spherical tipped stainless steelelectrodes having a V inch diameter were submerged into an open cup ofpropellants of compositions set forth in the above examples. Two sets ofelectrodes having spark gaps of 0.042 and 0.050 inch respectively wereused, both being connected to a 5000 volt, 6.0 microfrared variablecapacitance electrical system. Electrical energy was applied until aspark was generated across the electrodes and the propellant ignited.The total energy required for ignition of the propellants was computedfrom the formula, W== /2CV where W is total energy in joules, C iscapacitance in farads, and V is voltage applied in volts. The aboveprocedure was applied to testing propellants without the additive ofthis invention. Results of the foregoing tests are given in thefollowing table.

TABLE II.EFFECT OF ADDI'IIVES UPON SPARK IGNITION ENERGY ElectrodeVoltage System Energy Example No. Composition Gap, inches Applied, voltsCapacitance, Applied, Results Inicrofarads joules Base propellant: 60%Ethyl Nitrate, 40% Propyl 0.042 5, 000 6.0 No ignition.

Nitrate, no additive. 1 Base propellant: 60% Ethyl Nitrate, 40% Propyl0. 042 2,100 4.0 8.8 Ignition.

Nitrate, 1.5% by weight colloidal graphite added. 2 Base propellant: 60%Ethyl Nitrate, 40% Propyl 0.042 2,100 3.0 6. 6 Do.

Nitrate, 1.5% by weight tetra ethyl ammonium chloride added. 3 Basepropellant: 60% Ethyl Nitrate, 40% Propyl 0.050 3,000 1.0 4.5 Do.

Nitrate, 0.5% by weight tetra n-propyl ammonium nitrate added. Basepropellant: 60% Ethyl Nitrate, 40% Propyl 0.050 5,000 1.0 13 Noigmtion.

Nitrate, no additive. 4 Base propellant: propylnitrate,3.0% by weight0.050 2,700 2.0 7.0 Ignition. tetra n-propyl ammonium nitrate added.Base propellant: 100% propyl nitrate, no additive 0. 050 5, 000 6. 0 75N o ignition. an ethyl-propyl nitrate propellant without these additivesThe data in the foregoing table demonstrate the sigby means of a sparkgenerated between electrodes submerged in the propellant requires arelatively high electrical energy. This is attributed to the lowelectrical conductivity of the propellant. By adding a quaternaryammonium salt or colloidal graphite, an ethyl-propyl ninificantimprovement in spark ignition of non-conductive, organic liquidpropellants as a result of the addition there- 0 to of quaternaryammonium salts or colloidal graphite.

The data show that with the inventive additives the energy required togenerate an ignition spark is decreased by a Tetramethyl ammoniumbromide Tetraethyl ammonium bromide Tetraethyl ammonium chlorideTetra-n-propyl ammonium nitrate Tetra-n-propyl ammonium iodideTetra-n-butyl ammonium iodide Tetra-n-butyl ammonium picrate Since manyexamples of the foregoing compositions may be made without departingfrom the scope of the invention, the foregoing is to be interpreted asillustrative only, and not as defining or limiting the scope of theinvention.

We claim:

1. An improved liquid propellant consisting essentially of anelectrically non-conductive, nitrated organic liquid propellant and anadditive selected from the group consisting of quaternary ammonium saltsand colloidal graphite, said additive being present in an amounteffective to permit practical spark ignition of said electricallynonconductive nitrated organic liquid propellant.

2. An improved liquid propellant consisting essentially of a memberselected from the group consisting of ethyl nitrate, propyl nitrate, andmixtures thereof, and an additive selected from the group consisting ofquaternary ammonium salts and colloidal graphite in an amount of 0.1% to3.0% by weight.

3. A method for improving the spark ignition of an electricallynon-conductive nitrated organic liquid propellant, said methodcomprising adding to said liquid propellant an additive selected fromthe group consisting of quaternary ammonium salts and colloidal graphitein an amount efiective to permit practical spark ignition of saidelectrically non-conductive nitrated organic liquid propellant.

4. A method for improving the spark ignition of a liquid propellantselected from the group consisting of ethyl nitrate, propyl nitrate, andmixtures thereof, said method comprising adding to said liquidpropellant an additive selected from the group consisting of quaternaryammonium salts and colloidal graphite in an amount of 0.1% to 3.0% byweight.

References Cited UNITED STATES PATENTS 2,433,943 1/1948 Zwicky et al.l49-89 X 2,993,768 7/1961 Holzl 14989 X 3,116,187 12/1963 Scanlon et al.14989 X 3,148,214 9/1964 Smith 149-88 X 3,208,891 9/1965 Eschrich et al.149-89 X CARL D. QUARFORTH, Primary Examiner. S. J. LECHERT, 1a.,Assistant Examiner.

